Comprehensive genomic identification and multi-tissue transcriptomic profiling of vitamin D3-related genes in Atlantic salmon (Salmo salar)

The metabolic pathway of vitamin D3 is highly conserved across vertebrates, yet its specific organization in teleost fish remains poorly defined. This study characterizes the genomic repertoire and tissue-specific expression of 16 vitamin D3-related genes in Atlantic salmon (Salmo salar). By overcoming the limitations of automated annotation tools through manual curation and phylogenetic validation, we resolved multiple paralogs arising from the salmonid whole-genome duplication. Tissue profiling revealed unexpected regulatory strategies distinct from the mammalian paradigm. Notably, the skin lacked expression of the biosynthetic enzyme dhcr7, and the head kidney showed negligible expression of the activating enzyme cyp27b1 and the catabolic enzyme cyp24a1. These findings imply that vitamin D3 synthesis and activation in Atlantic salmon may occur in alternative tissue layers or rely on extra-renal mechanisms. Furthermore, the absence of a distinct GC ortholog points to serum albumin (alb2) as the functional transport protein. We also highlight the variability of common housekeeping genes across tissues, underscoring the need for rigorous reference gene validation in salmon transcriptomics. These results redefine our understanding of vitamin D3 metabolism in teleosts and provide a corrected genetic framework for improving dietary protocols in aquaculture.